1. Field of the Invention
This invention relates to a sealing structure of liquid crystal injection holes in a liquid crystal display device, particularly, to a sealing structure of the liquid crystal injection holes in the liquid crystal display device having a plurality of liquid crystal injection holes.
2. Description of the Related Art
In recent years, the uses of the liquid crystal display devices have been developed as display means for personal equipments and the like in various fields, and there is now a great demand for the liquid crystal display devices for the purpose of large scale displays.
In general, such a liquid crystal display device is manufactured as a display by connecting external electrodes to a liquid crystal cell and overlapping with needed polarizing plates.
On the other hand, the liquid crystal cell is manufactured by the procedures comprising the steps of forming transparent electrodes to be needed on an opposing inner surfaces of the upper and lower substrates made of glass or polymer films, printing an orienting agent or film on the surfaces formed with the transparent electrode and subjecting the resultant to a rubbing treatment thereon, generally, scattering bead-like plastic spacers having a diameter of about 10 .mu.m onto one of the inner surfaces of the upper and lower substrates while forming on the other of the inner surfaces a sealant of the flexible epoxy resin adhesive by screen printing, overlapping the upper substrate and the lower substrate with each other thereby to harden the sealant at a predetermined temperature, letting an air inside the cell out in the quasi-vacuum, and then filling the liquid crystal with the help of the atmospheric pressure from the liquid crystal injection holes provided in the cell by immersing the portion in which the holes are disposed, and sealing the liquid crystal injection hole with the sealing agent after the completion of filling.
In this case, if there is only one hole for injecting the liquid crystal, it requires a lot of time to fill the liquid crystal when the liquid crystal cell to be filled is large-scaled. Therefore, as is shown in FIG. 1 and FIG. 2, for example, there are provided a plurality of liquid crystal injection holes in such a manner that a pair of opening portion indicated as liquid crystal injection holes 134 are provided on sealant 132 of an end face of the cell, or in such a manner that a pair of holes as indicated as liquid crystal injection holes 144 are made on an end portion of either of the upper or lower substrate. After completion of filling the liquid crystal through respective injection holes, the liquid crystal cell is to be finished up by sealing the liquid crystal injection holes as to be the opening portions of a sealant 152 with a sealing agent 156 as shown in FIG. 3.
Now, in recent years, there have been an increasing demand for the liquid crystal display devices in various art fields, and the liquid crystal display devices are requested, to have performances endurable under circumstances applied in various conditions, as well as to be manufactured in low costs. However, the method by which a plurality of the liquid crystal injection holes are sealed individually, increasing the processing steps, can not achieve a reduction in cost. Furthermore, the sealing structure as shown in FIG. 3 sometimes gives rise to a problem in the quality of the liquid crystal display device.
In order to increase the reliability for sealing of the liquid crystal cell, as shown in FIG. 4, it is necessary to make the contact area of the sealing agent with the sealant of the cell as large as possible, or to inject the sealing agent into the cell as much as possible so as to resist and withstand the pressure of the liquid crystal caused in the cell by the external forces such as the pressing force and bending force exerted on the cell, or by change in temperature (refer to FIG. 5). However, the enlargement of the contact area by making the width of the sealing agent larger is restricted due to limitation of printing properties of the sealing agent or due to dimensional limit in design of the cell. Further, it is not easy to inject much sealing agent into the cell due to the pressure of the liquid crystal inside the cell, and even if sufficient sealing agent can be injected, since there is no escape for the liquid crystal in the cell, the caused pressure possibly makes the cell gap uneven, thus giving rise to the lack of the reliability in respect to the cell quality.